The present invention relates to crosslinked or networked polymeric gels and to methods of hydrocarbon production or recovery from underground formations using such networked polymeric gels, and, especially, to networked polymeric gels that are suitable to withstand high temperatures and/or high salt content/salinity (for example, commonly experienced in hydrocarbon/oil production and recovery) and to methods of using such gels in hydrocarbon/oil production or recovery.
Gelled or crosslinked water-soluble polymers have been widely used in enhanced oil recovery operations. For example, such gelled polymers can be used to alter the permeability of underground formations to enhance the effectiveness of water flooding operations. In a number of application, polymers and appropriate crosslinking agents or systems are injected in an aqueous solution into the underground formation. Preferably, the polymers permeate into regions having the highest water permeability and gel therein. Fluids injected into the formation in subsequent water flooding operations, are, for example, diverted away from the regions in which the gel formed to areas containing unrecovered oil.
It is generally desirable that polymers used in processes for the recovery of oil and other hydrocarbons impart to a liquid an increased viscosity when a relatively small quantity of the polymer is added. The increased viscosity is preferably achieved at a minimal cost. It is also desirable that such polymers form gels, for example, in the presence of a gelling agent such as a crosslinking agent, in the desired underground formations and do not gel before they can effectively penetrate the desired underground formations. Many processes have been developed to delay the gelation of gelling compositions by adding a delaying agent. However, such gelation delaying agents often add significant costs to oil field operation.
Although many polymers have been developed and used in hydrocarbon/oil recovery processes, many of these polymers cannot adequately withstand the hostile environments present in oil recovery. For example, many such polymer are incapable of forming gels having sufficient thermal stability, particularly in harsh environments such as in water containing high salinity.
Many polymer systems currently used in the oil recovery systems also include environmentally undesirable components. For example, in certain systems chromium crosslinking agents are used to produce gels of increased stability. However, a chromium salt is not an environmentally desirable compound and increased costs may be incurred to prevent contamination of ground water sources. Likewise, many conventional crosslinking systems include environmentally undesirable phenolic compound (known to be toxic) and/or formaldehyde (known to be a carcinogen).
It is desirable to develop water-soluble polymers that can be used to prepare crosslinked polymer networks/gels that withstand hostile environments such as those found in hydrocarbon/oil recovery.